This invention relates to a method of treating an unconsolidated formation surrounding a borehole.
Numerous processes have been proposed for consolidating subterranean formations surrounding a borehole to prevent sand particles flowing from an unconsolidated formation into the borehole with the fluids being pumped from the borehole. Migration of the sand particles not only fill in the borehole and cause deterioration of the walls of the borehole, but can cause considerable damage by flowing into the system removing the fluid from the borehole. If properly consolidated, the formation can act as a filter in that it permits the flow of the fluid into the borehole while holding back any loose particles which would be otherwise carried by the fluid flowing out of the formation. In areas where oil is too heavy to flow naturally into boreholes, large areas of the subterranean formation containing the heavy oil are heated by forcing steam down the boreholes and into the formations so as to reduce the viscosity of the oil. In this type of operation the consolidated formation must not only be sufficiently permeable to permit the flow of the oil into the borehole, but it must be able to withstand the flushing of steam from the borehole into the formation for long periods of time. While the known processes may be operable to develop at least some degree of consolidation, the resulting permeability may not be acceptable, the formation may not retain the consolidation, or the process may be expensive and may not be practical, for example, in a borehole which is not thermally completed well.
Prior processes have been described which involve injecting plastic materials into the unconsolidated sand so as to provide a resinous plastic material for bonding the sand particles together. U.S. Pat. No. 4,232,740, Nov. 11, 1980 of Jack H. Park proposes a method which requires contacting the sand with an aqueous solution of calcium hydroxide, plus an effective amount of calcium salt having solubility greater than calcium hydroxide, such as calcium chloride, plus an alkalinity agent such as sodium hydroxide. It is explained in the U.S. Patent that the well may be enlarged and sand of a preferable particle size or size range introduced into the formation prior to treatment.
U.S. Pat. No. 3,072,188, Jan. 8, 1963, of Richard A. Morse describes a method of heating a borehole of a well in which the borehole is packed with a refractory material and the borehole is heated by igniting a fuel-air mixture which has been injected into the borehole. The combustion which results is described as reverse combustion, i,e. the direction of movement of the combustion front through the permeable medium is opposite to the direction of movement of the fuel-air mixture and products of combustion. It is explained that a temperature of at least about 800.degree. F. may be necessary to cause hydrocarbons in the formation to coke.
U.S. Pat. No. 3,147,805, Sept. 8, 1964, of Robert J. Goodwin et al, disclosed a method of injecting a heated oxygen containing gas, which may contain a mixture of combustion products, into a borehole and increasing the temperature of the gas to thereby heat the formation to a temperature to form coke.
U.S. Pat. Nos. 3,254,716, June 7, 1966, of Benny M. Fitzgerald et al, and 3,974,877, Aug. 17, 1976, of David A. Redford both disclose a method of injecting a mixture of steam and air into a borehole to provide a consolidated formation, the steam being utilized in an attempt to avoid combustion occurring in the formation. U.S. Pat. No. 3,254,716 describes the injection being carried out for a sufficient time and at a temperature to form a bonding by the formation of coke. In the preferred method disclosed in U.S. Pat. No. 3,974,877 a sand or gravel pack is formed around a borehole and saturated with bituminous petroleum, and the pack is then subjected to an injection of a mixture of steam and air to form a coke like material.
Because the borehole is exposed to various substances, it is believed that formations which have been consolidated by the addition of plastic materials or treatment by various chemical substances may experience rapid deterioration or loss of permeability. The processes which utilize relatively high heat to achieve coking may result in an exceptionally hard and durable formation, but the resulting formation may not be sufficiently permeable to permit a good flow of fluid therethrough. The use of steam with hot air is not believed to be a satisfactory solution to avoid coking due to combustion because the steam has an abrasive action tending to weaken the consolidation. Moreover, the steam reduces the oil saturation around the borehole, and this results in a weaker formed consolidation immediately adjacent the borehole. Additionally, the use of steam with the air is not practical for wells which are not thermally completed.